A computational study of H2 dissociation on silver surfaces: the effect of oxygen in the added row structure of Ag110.

We studied computationally the activation of H(2) on clean planar (111), (110) and stepped (221) as well as oxygen pre-covered silver surfaces using a density functional slab model approach. In line with previous data we determined clean silver to be inert towards H(2) dissociation, both thermodynamically and kinetically. The reaction is endothermic by approximately 40 kJ mol(-1) and exhibits high activation energies of approximately 125 kJ mol(-1). However, oxygen on the surface, modeled by the reconstructed surface p(2 x 1)O/Ag(110) that exhibits -O-Ag-O- added rows, renders H(2) dissociation clearly exothermic and kinetically feasible. The reaction was calculated to proceed in two steps: first the H-H bond is broken at an Ag-O pair with an activation barrier E(a) approximately 70 kJ mol(-1), then the H atom bound at an Ag center migrates to a neighboring O center with E(a) approximately 12 kJ mol(-1).